Cold trap

ABSTRACT

A method of preventing corrosive gases from entering the vacuum pump of a vacuum and fill system that is used in conjunction with lamp manufacture. In performing the method a cold trap, which may be a flask of liquid nitrogen is interposed in the line between the vacuum pump and the vessel to be evacuated. During the vacuum and fill operations, unused amounts of fill gases such as bromine and iodine normally would be drawn from the lamp into the vacuum pump. When the flask of liquid nitrogen is interposed in the line, however, the gases are collected in the trap.

United States Patent 1191 ovio 1March 20, 1973 [5 COLD TRAP 3,103,108 9/1963 Santeler ..62/55.5 Inventor: Robert J Bovio, Lowell Mass. 3,216,207 11/1965 Boyer ..62/55.5

[73] Assignee: GTE Sylvania Incorporated Primary Examiner-William J. Wye [22] Filed: Aug. 5, 1971 Attorney-Norman J. O Malley-et a1.

[21] Appl. No.: 169,479 [57] ABSTRACT A method of preventing corrosive gases from entering [52] US. Cl ..62/55.5 the vacuum pump of a vacuum and fill system that is [51] Int. Cl. ..B01d 5/00 used in conjunction with lamp manufacture. In per- [58] Field of Search ..62/55.5 forming the method a cold trap, which may be a flask of liquid nitrogen is interposed in the line between the [56] References Cited vacuum pump and the vessel to be evacuated. During the vacuum and fill operations, unused amounts of fill UNITED STATES PATENTS gases such as bromine and iodine normally would be 1,307,999 6/1919 Buckley ..62/55.5 drawn from the p into the vacuum P P- when 2,317,814 4/1943 Schuchmann;.. ..62/55.5 the flask of liquid nitrogen is interposed in the line, 2,465,229 3/1949 Hipple ..62/55.5 however, the gases are collected in the trap, 2,831,549 4/1958 Alpert.. 62/55.5 2,837,318 6/1958 Wintem1 ..62/55.5 1 Claim, 1 Drawing Figure cow TRAP BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates, in general, to a method of manufacturing lamps and particularly to a gas trap for a vacuum system. Specifically, the invention relates to the collection of unused fill gases that would normally be drawn into the vacuum pump, thus damaging it.

In a normal sequence of operations in the making of a lamp, the lamp envelope is fixed to a receiving manifold on a vacuum system. A vacuum pump in the system is operated to evacuate the air from the lamp envelope prior to the appropriate fill gases, such as bromine, or iodine, etc. When the pumping operation is complete, the lamp envelope is then sealed and removed from the vacuum manifold.

2. Description of the Prior Art In conventional lamp manufacture procedures, a sequence of evacuation and fill steps are used to clean the envelope and include the gas. In most lamps the gas is placed inside the bulb to reduce filament evaporation and permit a high filament temperature. Different types of fills have been used over the years, such as argon, nitrogen and, more recently, bromine and iodine. The gases which were formerly maintained were at a pressure of 80 percent of atmospheric, that is, about 600 mm. of mercury. The pressure rose to approximately atmospheric when the lamp was operated. More recently, with the use of bromine and iodine gases, much higher pressures are produced and the lamp can be made more efficient in terms of lurnens per watt by increasing the filament temperature.

In the fabrication of a lamp where easily condensable gases are added, a condensed residue is left in the vacuum manifold head after a lamp is made. Thus, when the vacuum-manifold head is used for subsequent evacuations, this residue can be drawn back into the vacuum pump to contaminate it.

Normally, iodine and bromine are not corrosive in their elemental state, but .when they combine with water they can adversely effect the various portions of thesystem. Such water is present in the air which is evacuated from the envelope and, also, is present in the pump. Thus the gases can combine withv the water. present' in the system and corrode the working parts of the pump and harm them.

SUMMARY OF THE INVENTION trap system are free of the'corrosive sludge and only require monthly oil changes.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, a schematic view of a typical evacuation and fill system is depicted showing the cold trap positioned between the lamp and the pump.

DESCRIPTION OF THE PREFERRED EMBODIMENTS pump 12, and a cold-trap arrangement 14.

All of the abovementioned components are interconnected by a piping arrangement having appropriate inlet and outlets for maintaining the systempA fill gas inlet pipe 16 is directed to the base of the lamp manifold 10 for the purpose of supplying a necessary mixture of fill gas to the lamp 11. A pair of vacuum toggle-action valves 20 and 22 are positioned within the direct line from the manifold 10 to the pump. These valves 20 and 22 are opened during the evacuation phase to allow the air in the envelope to be drawn back to the pump 12.

Two similar type toggle-action valves 24 and 26 also are located along the piping-system. Valve 24 controls an air pressure line and valve 26 controls an exhaust line. The operational sequence of these valves will be described hereinafter. v I

As seen in the drawing, the piping system is interrupted by the cold-trap arrangement 14. This comprises an openended pipe 30 that is centrally positioned within one leg of a T-shaped trap 32. The pipe is sealed at 34 to the trap 32, and the other leg of the trap is rejoined to the piping system. As seen in the drawing, the extension of the pipe 30 and the trap 32 is positioned within a flask of liquid nitrogen. With this arrangement, air drawn from the envelope Ill by pump 12 will be carried through the pipe 30, and due to the temperature of the liquid nitrogen surrounding the pipe the gas will solidify.

A brief description of a sequence of evacuation and fill steps will now be given to fully describe the novelty of the. invention. A lamp structure 11 to be evacuated the line. An open end of the trap is immersed in a flask filled with liquid nitrogen or other suitable gas which boils below about l95.8 C. With this arrangement, any residue gas left in the manifold is drawn back toward the pump and in its travel is crystallized and held in the trap area by virtue of the liquid gas. It has been found that the vacuum pumps using this type of and filled with appropriate gases is first attached to the vacuum manifold 10. The valves 24 and 26 are closed and valves 20 and 22 are opened to provide a path through the piping from the manifold 10 tothe pump 12. The pump 12 is then activated until the desired vacuum is attained in the envelope 11. Valve 20 is then closed off so that a mixture of fill gas can be administered to the envelope by way of inlet 16. When the proper gas fill pressure is met, the lamp 11 is sealed at the exhaust stem 40. The finished lamp 11 can then be removed from the manifold 10.

After the previous lamp stern has been removed from themanifold head 10, a new lamp is then attached to the manifold for a sequence of evacuation and fill operation.

At the outset of the first pumping of a new lamp envelope, a residueof gas left from the last gas fill operation is present within the manifold area. On the initial vacuum surge of the first operation of'the pump, this gas will be drawn toward the pump 12. As the gas enters the trap area 14 over pipe 30, the gas crystallizes due to the temperature of the liquid nitrogen. The crystals of gas will be collected on the interior of pipe 30, thus only air will be drawn back to the pump 12.

After many subsequent lamp fabrications, a build-up of the crystals will develop in the cold trap 32. This build-up of crystals can easily be removed without cleaning the pump. Removal of the crystals from the trap 32 is accomplished by removing the flask 36 from pipe 30 and closing valves 20 and 22 and opening valves 24 and 26. Valve 24 allows high pressure air to be forced through the trap 30 and out the exhaust valve 26.

SPECIFIC EXAMPLE The extended exhaust tube of a lamp having a filament structure is inserted and locked into a vacuum head of a manifold. A series of vacuum pumping operations is initiated; the first pumping is considered a rough pump and is in the vicinity of 25 microns. Thereafter a flame is directed to the lamp envelope and its exhaust tube, while a second vacuum pumping of about torr is established. The flame is terminated and the lamp envelope flushed with nitrogen and the filament structure is lit at 60 Volt A.C. for one minute. This lighting sequence tends to clean the filament of any residue. After a short wait, the envelope is again flushed with nitrogen to clean out the residue from the envelope. Thereafter the envelope is filled with 800 mm of nitrogen. A second lighting of the filament is made at Volts A.C. This second lighting determines the lighting characteristics of the lamp. After lighting for approximately twenty seconds, the nitrogen in the lamp envelope is evacuated. The lamp is then completely immersed in liquid nitrogen and a fill of 8 mm. Hydrogen bromine is made to the lamp. After a few minutes the gas is condensed. The lamp envelope is further pressurized by the introduction of 225 mm. of nitrogen. A tipping off or the sealing of the exhaust tube is then made.

I claim:

1. A vacuum system comprising: a vacuum manifold; a vacuum pump; a cold trap; a piping system interconnecting said manifold to said pump through said cold trap; a flask of liquid refrigerant within which a portion of said cold trap is immersed; a first pair of valves located within said piping system with one of said valves located adjacent to said vacuum manifold and the other of said valves located adjacent to said vacuum pump whereby communication within said piping system between said manifold and said pump may be regulated; a second pair of valves located within said piping system intermediate the valves of said first pair of valves, one of the valves of said second pair of valves being connected to a source of air under-pressure and the other valve of the said second pair of valves being connected to an exhaust whereby said piping system intermediate said manifold and said pump, including said trap, may be flushed. 

1. A vacuum system comprising: a vacuum manifold; a vacuum pump; a cold trap; a piping system interconnecting said manifold to said pump through said cold trap; a flask of liquid refrigerant within which a portion of said cold trap is immersed; a first pair of valves located within said piping system with one of said valves located adjacent to said vacuum manifold and the other of said valves located adjacent to said vacuum pump whereby communication within said piping system between said manifold and said pump may be regulated; a second pair of valves located within said piping system intermediate the valves of said first pair of valves, one of the valves of said second pair of valves being connected to a source of air under pressure and the other valve of the said second pair of valves being connected to an exhaust whereby said piping system intermediate said manifold and said pump, including said trap, may be flushed. 